An engineer shows a plastic model of the Covid-19 coronavirus at the Quality Control Laboratory at the Sinovac Biotech facilities in Beijing.

Nicolas Asfouri | AFP | Getty Images

A potential coronavirus vaccine developed in China appeared to provoke neutralizing antibodies in dozens of patients in an early-stage clinical trial, an important step in developing a vaccine that might provide immunity to Covid-19.

The vaccine candidate also induced binding antibodies in most of the patients within 28 days and appeared to be safe and well-tolerated, according to the findings of the phase one trial published Friday in The Lancet.

“These results represent an important milestone,” Wei Chen, a professor at the Beijing Institute of Biotechnology and who led the study, said in a press release. “However, these results should be interpreted cautiously. The challenges in the development of a Covid-19 vaccine are unprecedented, and the ability to trigger these immune responses does not necessarily indicate that the vaccine will protect humans from Covid-19.”

The potential vaccine from CanSino Biologic, called Ad5-nCoV, was approved for human trials in March. The participants were ages 18 to 60 and received a low, medium or high dose. There were 36 people in each of the three groups of low, medium and high dosages.

The concentration of neutralizing antibodies, which researchers believe is important in acquiring protection against the virus, appeared to increase with dose strength, they said. By day 28, half of the patients in the low- and middle-dose groups showed neutralizing antibodies compared with three-quarter of patients in the high-dose group.

The researchers noted the small sample size and said further research will be needed before this vaccine can become available.

Moderna said its potential vaccine produced neutralizing antibodies for eight of the patients whose data was available so far. Additionally, all 45 patients in the study produced binding antibodies seen at similar levels of people who have recovered from the virus, the company said.

There are no proven treatments for Covid-19. Scientists are optimistic a vaccine to prevent the disease will be ready in the first half of 2021 — 12 to 18 months since Chinese scientists first identified the coronavirus and mapped its genetic sequence.

More than 100 vaccines are under development globally, according to the World Health Organization. At least eight vaccines are in human trials.

Scientists hope the antibodies provide some degree of protection against getting Covid-19, but they can’t say that definitively since it hasn’t been studied and some patients appear to have been reinfected after recovering from the virus.

In the CanSino Biologic vaccine trial, most patients typically reported pain at the injection site and others reported fever, fatigue or a headache, the Chinese researchers said. One participant who received the higher dose reported severe fever along with severe symptoms of fatigue, shortness of breath and muscle pain. The reactions persisted for less than 48 hours.